Water Regime Changes and the Function of an Intermittent Wetland

Abstract

The intermittent Lake Cerknica comprises a variety of wetland habitats, which support numerous species, many of them included on the Red List. The exchange of wet and dry periods influences the through-flow of energy and the turnover of matter in the lake. In the last five decades, the water level fluctuations were highly variable. Since 1961 the May and June water levels have shown a decreasing trend line, in October the trend line revealed an increase, while from November to February no changes of trend could be observed. High water levels in winter and during the peak vegetation season negatively affected reed productivity. The decomposition of reed leaves increased with the wetness of the survey location, while the soil mineralisation rate was only slightly related to soil wetness. In comparison to the tributaries, the lake water contained relatively low amount of nutrients, which was a consequence of a densely vegetated area.Keywords Decomposition · Evapotranspiration · Intermittent lake · Phragmites australis · Wetland habitats IntroductionLake Cerknica is an intermittent wetland appearing at the bottom of the Cerknica polje karst depression. It is characterised by extreme inter-annual water level fluctuations, which are the result of a high precipitation rate and water runoff into an extensive underground drainage system in carbonate rocks. The catchment area of the lake extends over 475 km 2 . The majority of the lake's inflow consists of karstic waters (80%), while only one tributary brings surface water (15%). The amount of water in the lake depends on precipitation and potential evapotranspiration of the

Seasonal patterns of Phragmites australis breakdown in a karstic freshwater system (Doberdò Lake, Northeast Italy) in relation to water level fluctuations, environmental features, and macrobenthic invertebrate communities

“…Pulsating variations in the hydrological regime constitute the second main factor driving dynamics in Doberdo `Lake. These typical variations, similar to those observed in Cerknica Lake, may also play a pivotal role in shaping floral and faunal communities (Cronk & Fennessy, 2001;Gabersc ˇı ˇk et al, 2003;Dolinar et al, 2011;Dolinar et al, 2016). Water level changes in Doberdo `Lake strongly correlated with the changes in the hydrometric Soc ˇa River level (Figs.…”

Water Level Fluctuations and Air Temperatures Affect Common Reed Habitus and Productivity in an Intermittent Wetland Ecosystem

“…Water movement represents a physical force that can break reed culms and prevents the passive and humidity-induced aeration of the rhizome system at higher water levels, which also occurs via dead stems [16,42]. In water fluctuating systems, reed stands are frequently subjected to prolonged dry periods [21]. The common reed can withstand longer periods of water shortage through a reduction in leaf area and by an increased water-use efficiency [43].…”

Water-level fluctuations as a driver of Phragmites australis primary productivity, litter decomposition, and fungal root colonisation in an intermittent wetland

“…1. The water levels in the reed stands at Zadnji kraj are closely related to those at Gorenje Jezero (Dolinar et al, 2011a), although there are differences in the sediment moisture during dry periods, due to the higher organic matter content at Gorenje Jezero (Dolinar & Gaberš-čik, 2010) and the presence of hyporeic water due to the vicinity of the Stržen watercourse.…”

“…Throughout each year, the Cerkniško polje depression is flooded for *9 months and dry for *2 months, usually in summer. However, the water regime varies significantly across the years (Kranjc, 2003), and thus Lake Cerknica composes of diversified habitats which change in time and space (Dolinar et al, , 2011a. The vegetation patterns show clear zonal distributions that depend on the extent and frequency of the flooding (Dolinar et al, 2011a).…”

“…Wetlands are threatened by the alteration of hydrological conditions, especially by intermittent changes of water levels, which affect their functions and succession, in terms of primary productivity, turnover rate, and interactions among species (Cronk & Fennessy, 2001;Dolinar et al, 2011a). Wetland primary productivity is greatly influenced by the flooding duration and frequency (Hudon et al, 2005).…”